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Chapter 4: Measures of Position
By observing a box plot, important information concerning the distribution
of the data set can be obtained. A summary of the potential information
which can be obtained from a box plot is given next when considering the
position of the median and the length of the whiskers.
Information which can be obtained from a Box Plot – Looking at
the Median
If the median is close to the center of the box, the distribution of the data
values should be approximately symmetrical.
If the median is to the left of the center of the box, the distribution of the
data values should be positively skewed.
If the median is to the right of the center of the box, the distribution of
the data values should be negatively skewed.
Information which can be obtained from a Box Plot – Looking at
the Length of the Whiskers
If the whiskers are approximately the same length, the distribution of the
data values should be approximately symmetrical.
If the right whisker is longer than the left whisker, the distribution of the
data values should be positively skewed.
If the left whisker is longer than the right whisker, the distribution of the
data values should be negatively skewed.
Figure 4-23
graphically illustrates the above observations for the median
and the length of the whiskers for box plots.